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Thread: danaher servo encoder quandry - rs485 data?

  1. #1

    Default danaher servo encoder quandry - rs485 data?

    I picked up a surplus servo motor recently, without knowing the details of it's functionality.

    Now, with the motor in hand, I've been researching, and this model (a Danaher Motion servomotor) appears to be equipped with a so-called "smart feedback device" (SFD), which communicates via rs-485 data link. Here's what information I have ATM:

    ----Specifications of the SFD RS-485 link----
    Signaling: RS-485 differential, 8 bit data with odd parity compatible with standard UARTs
    Baud rate: 2.5 MBaud
    Data rate: 2.5 10^6 Symbols/s 8 bits/Symbol = 20 MBits/s
    Update period: once every 51.2 s new position sample
    Error detection: 5 bit CRC in addition to parity check

    Frankly, I have no idea what to do with it at this point. The associated servo drive from danaher fits neither my needs nor my price range, so I'm thinking I would have to translate this into a quadrature signal by some means?

    If anyone has experience with this type of encoder, or could point me towards some relevant source of information (so I at least know what I'm getting myself into), it would be much appreciated.

    -b2b

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  2. #2
    Registered vger's Avatar
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    You will probably find it easier to just replace the encoder with a standard quadrature encoder.

    The installed encoder communicated with it's drive via RS-485 serial link, similar to RS-232 but higher speed capacity with the differential signal. There are RS-232 to RS-485 converters (I have one I use with ABB VFD drives) but you would still have serial data (absolute position data) to deal with.

    Steve



  3. #3

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    I sell that motor and that encoder

    It is NOT an encoder; it is actually a resolver with a small pcb that converts the absolute resolver data into a proprietary serial data stream that the drive decodes. It is called smart because on power up it spits out the motor part number, the drive tuning data, the motor absolute position within 1 rev, previously stored on an internal EEPROM. It has very high bandwidth for higher performance than most simple TTL quadrature encoders. With it 800hz velocity loop bandwidths are possible (normal non Kollmorgen servo drive will usually get to around 100-150hz max). Unless you use a Kollmorgen drive (S200, S300, AKD) that accepts this feedback you will likely not be able to use it.

    That said, vger is probably right; replace it with a regular quadrature encoder to use it with a non Kollmorgen drive. We supply those same motors with this SFD, TTL quad, 1Vpp sine, and resolver feedback so you should be able to find another feedback of your choice to fit it relatively easily.

    Not sure why you would say the Kollmorgen drives to run this motor wont do want you want; there are so many possible choices I cannot imagine not finding one that will do your job. depending on the motor size, the drives that accept SFD feedback are as low as $ 410.00. pm me if I can help you.



  4. #4

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    Thank you both for your input.

    Further reading has reinforced the idea it would be folly to try to translate the provided data into quadrature.

    I also saw a used Kollmorgen s200 on ebay that wouldn't destroy my budget. My comment about not fitting my application refers to the fact that I'm working up to building a DIY-style CNC, not any sort of production machine.
    I was planning to get 3 Granite Devices VSD-E's (if you're familiar) with which I could power a variety of surplus drives, as I find them. I've got a couple steppers, and also two 3kw servos. The VSD-E can run both, though it can't push the big servos anywhere near their limits. Buying a purpose built servo drive for a single motor doesn't really fit my upgrade path.

    Kilroy, you mention that you're familiar the s200. Perhaps you can clear up a couple Q's. As I mentioned this is a DIY build, software controlled, probably emc2. Would the s200 work in that capacity? I've been trying to dig through all the documentation for these models just to find out how to connect the thing to a PC. I don't think Kollmorgen is marketing to the DIY audience.
    The used model I saw (s20360-srs) fits my drive perfectly power wise, but the 'srs' option seems to indicate some kind of connection called 'SynqNet'. I'm not interested if I have to buy a bevy of special purpose hardware. If I could plug it in and get it running without too much pain it might still be an option. Is it true that the s200 runs off of AC power and doesn't need an external DC supply? That would be a plus.

    This is my first build, so I'm really feeling my way in the dark here, especially when it comes to the industrial-level stuff, where it seems like every device is just a piece of a puzzle, and unless you have the rest of that puzzle, a particular part can be less than useful.

    I won't be mounting any other encoders. This motor is probably too small and too fast to be well suited to any axis on my CNC, and it would be a waste to split up this pretty little motor and cludge it together with some cheap encoder. If I can't find a convenient option I'll probably resell it.



  5. #5

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    Quote Originally Posted by born2bewilder View Post
    ...Kilroy, you mention that you're familiar the s200. Perhaps you can clear up a couple Q's. As I mentioned this is a DIY build, software controlled, probably emc2. Would the s200 work in that capacity? ......

    The used model I saw (s20360-srs) fits my drive perfectly power wise, but the 'srs' option seems to indicate some kind of connection called 'SynqNet'. I'm not interested if I have to buy a bevy of special purpose hardware. If I could plug it in and get it running without too much pain it might still be an option.

    Is it true that the s200 runs off of AC power and doesn't need an external DC supply? That would be a plus.

    This motor is probably too small and too fast to be well suited to any axis on my CNC
    There are versions of the S200 that are position indexers, plain velocity, and current loop drives; the position ones (s2xxx-CNS) can accept step&dir commands from the emc2 or mach3. the velocity or torque mode ones (-vts) accept +/-10v analog command instead. The -srs won't work as on power up it requires a handshake from the synqnet bus to wake up; until it rcvs that it is dead.

    There are both dc input (20-90vdc) and ac input (120, 120 voltage doubler, 240) models.

    And don't discount this motor just because it has a top speed of 6 or 8000rpm; it can just as well run at 1 rev per day with full torque if the drive & feedback is good.



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